Franken UPS

This is a 3000W inverter based UPS I will use as a backup supply for my server rack, gaming pc and lights

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As with allot of projects this one was born out of necessity. When a recent collapse of a coal storage silo at a major power plant left South Africa with a temporary shortage of power and rolling blackouts I decided it was time to build a monster uninterrupted power supply.

And so the Franken UPS was born. This is nothing that has not been done before but given my limited metal fabrication skill it will be somewhat of a challenge to build the frame for the batteries, inverter and charger.

Onto the specification:

4 x 70Ah 12V Batteries (Total of 280Ah capacity)
1 x 40A 12V Battery Charger
1 x 3000W Pure Sign Wave Inverter
12h run time
Color: Matt Black

Some notes:

I made the choice to go with a True Sign Wave/Pure Sign Wave inverter as opposed to a Modified Sign Wave inverter because I want the cleanest AC signal possible given that I will be running my surround sound speakers from this and don't want any unnecessary hum.


The Franken UPS is a simple unprintable power supply based on a set of car batteries, a 3000W True Sign Wave/Pure Sign Wave inverter and a battery charger. With rolling blackouts a reality in South Africa due to the recent collapse of a primary power station coal storage silo I needed something that could power my server rack and all its equipment, my gaming pc, a TV and some lights for at least 10 hours.

My design needed a movable trolley with a modular stackable design so that I could move it arround and add more battery packs if required in the future. In reality we do not have black outs that often and they do not last longer than 6 hours so I would not need to drain the batteries to empty regularly so I settled for cheaper car batteries instead of deep cycle batteries.

I had run a similar setup for a while using 2 card batteries and a small 6A charger but the charging time was ridiculous and without a neat frame or cabinet the solution was just sitting on the floor all the time irritating the hell out of me.

Run Time:

If my calculations are correct the 3000W inverter draws 13.63Ah at full load so in theory with the 4 series connected car batteries I have 240Ah capacity available giving the theoretical running time as 17 hours.

  • 4 × 70Ah Car Batteries 12V Lead Acid Maintenance Free
  • 1 × 40Ah Battery Charger 12V 40Ah battery charger with remote display and control
  • 1 × 3000W Inverter 3000W 220V AC Pure Sign Wave inverter
  • 4 × 25mm Square Tubing 6m x 25mm x 2mm Squire Tubing
  • 1 × 10M Foam Padding Tape 10M x 15mm Foam Padding Tape

View all 10 components

  • Log 20/01/2015

    Dewet01/20/2015 at 07:35 0 comments

    Some nice photos of the finished UPS. Notice how I cannot weld to save my life..... But it came out ok.

  • Log 14/01/2015

    Dewet01/14/2015 at 19:23 0 comments

    It's been almost 2 months that I have been running the Franken UPS trough everything that our power utility could trough at me (or the lack thereof depending on your view). Still waiting on some proper battery fuses to come from eBay but I'm considering this one done. If anyone wants the schematic for connecting something like this for automatic fail over I will be happy to spend the time on Eagle but until then it should be really easy to wire up using a rely/contractor.

  • Log 13/11/2014

    Dewet11/13/2014 at 10:44 0 comments

    Just completed the frame and basic wiring. This allows me to charger the batteries while I work on the last cable from the batteries to the inverter. In the picture you can see the setup so far. Always hard to think you can go from a pile of seemingly random things into complete build withing a few hours of work. So satisfiying!

View all 3 project logs

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Paul Leskinen wrote 06/05/2015 at 12:28 point

Does this work as a true "uninterruptable" power supply? I've kind of wanted to build one myself; but wouldn't you need to sync the inverter with mains frequency so that when you cut over, it is in phase? Likewise when mains recover, you'd have to speed up or slow down the inverter frequency until it's back in sync with the mains and then switch back over. I think that's what commercial UPS's do.

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davedarko wrote 11/15/2014 at 03:24 point
I just wondered with all the the critics of solar and wind power, why no one ever would think of using UPSs for each household instead of building huge power storage devices for not windy but clouded days. All our technical devices are that much better at saving power and not so wasteful anymore. Anyway, great idea!

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Dewet wrote 01/14/2015 at 19:16 point

Thanks davedarko. This project worked out significantly cheaper without adding the solar component to it. For now this works a treat and no sunny days required.

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Paul Leskinen wrote 06/05/2015 at 12:30 point

Tesla has announced a household battery that would be very effective as a home UPS, as well as being able to even out energy consumption (e.g. charge at night when rates are typically lower). But regardless of the scale (utility vs. home), there would need to be an enormous amount of storage deployed to soak up irregularities with renewable sources. Eventually, that problem must be addressed, as fossil fuels will not last forever.

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Gary wrote 06/27/2015 at 17:54 point

Most UPS are junk and meant to keep a device power for a very short period of time.  Would people dont understand just how much power most devices take and how big a UPS would need to be to run it for "days"

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